In order for, by way of example, two users in a radio communication system to be able to use their radio communication appliances to converse with one another or to interchange other user data, a “circuit-oriented”(“circuit switched”) telephone connection is usually set up between these two radio communication appliances using their air interfaces to the radio network. This circuit-oriented telephone connection allows the users of the two radio communication appliances to speak and to listen simultaneously (i.e., to communicate at the same time), using the “full duplex” method (i.e., in the forward and back transmission directions). In this case, the respective circuit-oriented telephone connection which has been set up between the radio communication appliances connected is maintained even if none of the users of the radio communication appliances connected is speaking or, considered in general terms, is transmitting user data. The telephone connection between the two radio communication appliances thus remains continually set up until one of the radio communication appliances actively initiates cleardown of the telephone connection.
By contrast, a “push-to-talk” (PTT) service is advantageous in practice for many communication situations. Such a PTT service involves a number of radio communication appliances, which means that they form a specific PTT group. In this context, only a respective one from a number of connected radio communication appliances simultaneously has an associated transmission authorization for transmitting or sending user data, particularly voice messages, to the remaining radio communication appliances connected to the PTT service. The user of a radio communication appliance is allocated the transmission authorization in this case, by way of example, by virtue of his/her actively requesting it from his/her appropriate network PTT server by pressing a special PTT key on his/her radio communication appliance. If this user presses the PTT key on his/her radio communication appliance first as compared with the other users connected to the PTT service, then he/she is granted the transmission or sending authorization to transmit a voice message or other user data to the other radio communication appliances connected by the PTT server as priority. While he/she keeps the PTT key pressed, only he/she has the transmission authorization allocated by the PTT server, while the ability to send is disabled for the users of the remaining radio communication appliances connected. In this case, the voice or user data are distributed in the radio network, while the sender is actually speaking, from the latter's radio communication appliance to the receiving radio communication appliances in the PTT group virtually in real time, particularly via the appropriate PTT server (streaming). In particular, the PTT server can, in this context, prescribe a maximum authorization period within which sending is possible only for the currently authorized sender. While voice or other user data are being sent by the respective radio communication appliance with authorization to transmit, the other connected radio communication appliances in the same PTT group can merely receive the voice or user messages sent by the radio communication appliance with authorization to transmit, and cannot themselves send or deliver their own voice messages using the PTT server. Only when the user with the current authorization to transmit lets go of or releases the PTT key on his radio communication appliance does he/she relinquish his/her exclusive authorization to transmit. The PTT server then preferably reallocates this authorization to that radio communication appliance whose user pressed the PTT key on his/her radio communication appliance next. In other words, when a voice message is sent by the respective radio communication appliance with authorization to transmit, the remaining radio communication appliances connected to the PTT service only listen to this voice message and cannot interrupt the user of this transmitting radio communication appliance.
In this way, the PTT service makes it possible for just a single radio communication appliance from the group of radio communication appliances connected to the respective PTT service to be able to dispatch or send a voice message or other user data to the radio communication appliances simultaneously using the “half duplex” method without being able to be interrupted by them in the process. Preferably, the respective user of a particular PTT service who has authorization to transmit is able to send one or more receiving radio communication appliances, as members of this PTT service, a voice or user message simultaneously and virtually in real time after he/she has pressed a special PTT key on his radio communication appliance. The users of the one or more receiving radio communication appliances connected to the PTT service are subsequently able to send a response in a corresponding manner when the PTT key has been let go on the radio communication appliance which currently has authorization to transmit. To this end, in turn, only a respective one of the radio communication appliances ready to respond is allocated authorization to transmit by the respective appropriate PTT server, while all the remaining connected radio communication appliances in the PTT group are merely able to receive this response message and are disabled for sending a response while it is being transmitted. Any radio communication appliance which belongs to the same PTT group and wishes to dispatch a voice message or user data is allocated authorization to transmit, on requesting it from the network's appropriate PTT server, in a corresponding manner by the latter, during which the remaining connected radio communication appliances in the PTT group are merely authorized to receive. It may be expedient, in particular, for the user of the respective, receiving radio communication appliance in the PTT group to be able to send voice messages or user data to the PTT server during the actual period of authorization of the respective radio communication appliance with authorization to transmit, or for the PTT server to continue to block forwarding of the voice messages or user data and to perform buffer-storage. Only when the transmission has ended or the maximum permitted authorization period for the current radio communication appliance with authorization to transmit has expired is the allocation of the transmission authorization by the appropriate PTT server controlled such that the latter forwards buffer-stored or current voice messages from that radio communication appliance whose user pressed the PTT key next before any of the other members of the PTT group. In this way, the PTT service is similar, from the user's point of view, to the known “walkie-talkie” service associated with conventional CB radio. Unlike the latter, however, the respective radio communication appliance with authorization to transmit can now also use the radio network in the respective radio communication system to address distant radio communication appliances which are registered with the same PTT service. In particular, the radio communication appliances logged onto the respective PTT service may be in different radio cells in a radio communication system.
Expediently, the maximum permissible authorization period for the transmission right can be set at an upper time limit by the PTT server. In that case, the user of the respective radio communication appliance with authorization to transmit is able to send voice or user messages to the remaining radio communication appliances connected only up to this maximum permissible upper time limit, even if he/she continues to keep his/her PTT key pressed. Furthermore, the respective radio communication appliance may be connected to a number of PTT services simultaneously.
For modem radio communication systems, it is desirable, in particular, to implement such a PTT service on a packet switched basis. In radio communication systems, this is preferably done using the IP multimedia subsystem (IMS) or a suitable system for implementing this. Appropriate activities in this regard are performed on international standardization committees, such as “Open Mobile Alliance (OMA)” and “3rd Generation Project Partnership (3GPP)”.
While the full duplex principle of the circuit-oriented telephone connection between two respective radio communication appliances promotes reciprocal, simultaneous interchange of voice messages and other user data in the forward and back directions, the half duplex method of a PTT service supports the sporadic dispatch of a voice message or of other user data by a single radio communication appliance in the PTT group of this PTT service simultaneously to all members of this PTT group in the forward direction only. If a member of the respective PTT group wishes to make a voice announcement to all other members of this PTT group, then he/she can do so spontaneously after operating a special PTT key, for example. As such, radio resources and radio network resources are used, with a corresponding resultant cost, only if a voice message is actually sent within the PTT group.
A typical instance of application for the PTT service arises, by way of example, when the organization control center in a logistics company wishes to make contact with one or more of its HGV drivers now and again in order to give new instructions. Conversely, it is desirable for the respective HGV driver to return a short voice message or response to the organization control center every now and then. To allow this sporadic sending of voice messages, a PTT session is continuously maintained between the organization control center and the respective HGV driver during work hours. If one of the HGV drivers connected or the organization control center wishes to make a voice announcement to the other connected members of this PTT group, such can be done spontaneously after respectively operating the PTT key on his/her/its radio communication appliance, for example. As such, radio resources and capacities in the radio network are engaged only if voice messages or user data are actually being sent by the respective radio communication appliance with authorization to transmit. In general terms, a PTT session is expedient when, from the point of view of time, voice messages or user data are being sent only now and then, and always in one particular direction of transmission. By contrast, it would be too complicated and too time-consuming in such cases to set up respective individual telephone connections between the respective radio communication appliance with authorization to send and all other receiving radio communication appliances in the respective PTT group involved. Such telephone connections set up on a continuous basis would be too expensive and would engage too much transmission capacity in the radio network and particularly on the air interface for the radio communication appliances connected.
If, by contrast, it is desirable not only to send a single voice message from the respective radio communication appliance to all other radio communication appliances in the respective PTT group in the forward direction, but rather to have a reciprocal discussion or conversation between at least two connected radio communication appliances simultaneously in the forward and back directions, then a PTT session's properties in connection with the half duplex transmission method are more of a drawback. This is because anyone wishing to use his/her radio communication appliance to dispatch a voice message to the other radio communication appliances in a PTT group disables dispatch of a voice message by the receiving radio communication appliances during the transmission period. The receiver thus cannot interrupt the sender or cannot cut him/her short if he/she is currently saying something. In addition, anyone wishing to dispatch a voice message is, in practice, given authorization to speak only if he/she has previously pressed a “PTT key” on his/her radio communication appliance. These are factors which are disadvantageous during a discussion or in the course of a conversation, wherein a telephone connection between the radio communication appliances connected would be more suitable.
The present invention is directed toward providing a way in which the user of a radio communication appliance can be provided flexibly and conveniently with a communication connection which is matched to the respective communication situation.